Optimization of Placement of Flow Control Devices under Geological Uncertainty in Steam Assisted Gravity Drainage

Abstract

Steam chamber conformance in Steam Assisted Gravity Drainage (SAGD) influences the efficiency and economic performance of bitumen recovery. Conventional SAGD well completion designs provide limited control points in long horizontal well pairs leading to development of a non-ideal steam chambers. Developing advanced wellbore completions and optimizing downhole tool settings is critical to achieve optimal steam distribution in heterogeneous reservoirs for optimal recovery. This paper presents a workflow to optimize SAGD well completion design by using flow control devices (FCDs). Optimum FCD placement, and specifications are determined in consideration of reservoir heterogeneity. Uncertainties in spatial distribution of facies and rock types, reservoir rock and fluid properties are represented by multiple equiprobable deterministic and stochastic geological realizations using Monte-Carlo simulation. The methodology is based on constrained nonlinear optimizationtomaximize the net present value (NPV) as the objective function. A coupled wellbore/reservoir simulation model of a well pad is implemented in the study, and the efficacy of different scenarios with varied well designs are assessed from evaluating bitumen production, steam injection, and well completion expenses. Results indicate superior performance of the wells equipped with FCDs compared to conventional concentric and parallel dual string well completion designs. For the cases examined, this translates to an average 7% increase of the expected NPV for different well completion designs when using FCDs. Furthermore, results show using zonal isolation in the well design is essential for compartmentalized reservoirs such aspoint bar deposits with their significant heterogeneity. Advanced wellbore completions provide sufficient tools to constrain steam injection and liquid production into and from different well segments, and manage steam chamber conformance along the horizontal well pairs, improve production efficiency, increase bitumen recovery, and reduce operating costs. A novel workflow is presented to optimize advanced wellbore completions utilizing flow control devices. This integrated assisted optimization approach considers uncertainties in geological properties, and determines the optimal FCD parameters and well completion design with acceptable computational effort. This integrated workflow allowed us to undertake a thorough evaluation of the key subsurface uncertainties, and design an overall development plan. The probabilistic nature of the results legitimize quantifying the uncertainties and identify associated risks for different completion strategies.